1. Field of the Invention
The present invention relates to a transmitter, the method of the same, and a communication system.
2. Description of the Related Art
Multipath fading is a phenomenon that makes reliable wireless transmission difficult. Diversity combining techniques combine the signals from multipath antennas is a way that mitigates fading. In most scattering environments, antenna diversity is a practical, effective and hence a widely applied technique. The classical approach is to use multiple antenna at the receiver and perform combining or selection and switching in order to improve the quality of the received signals.
In recent researches, space-time block coding using multiple antennas has been studied, and space-time codes have been introduced to improve the performance of mobile communication systems.
On the other hand, adaptive beamforming using antenna arrays has been widely used to reduce interference and mitigate multipath fading, hence improve the capacity. Adaptive arrays cancel multipath components of the desired signal and null interfering signals that have different directions of arrival from the desired signal. An extension of the space-time transmit diversity approach to the case of beamforming using two distinct beams was proposed in a paper of Katz, M., J. Ylitalo, “Extension of space-time coding to beamforming WCDMA base stations”, in Proc. IEEE VTC' 2000-Spring, pp.1230–1234, May 2000. It was shown that, when transmitting with two space-time encoded beams, the downlink performance is improved compared to the conventional single beam and two antenna transmitting scheme.
As described above, in conventional researches space-time block coding using multiple antennas and adaptive beamforming using antenna arrays for mitigating multipath fading have been developed separately.